Golf will be an Olympic sport this summer for the first time in 112 years—but not if there are no golfers to compete.

Pro golfers are rapidly dropping out of the Summer Games in Rio, set to begin in August.

The tally as of July 11 is up to 17 golfers: Jason Day (Australia); Brendon de Jonge (Zimbabwe); Branden Grace (South Africa); Miguel Angel Jimenez (Spain); Dustin Johnson (America); Marc Leishman (Australia); Hideki Matsuyama (Japan); Graeme McDowell (Northern Ireland); Rory McIlroy (Northern Ireland); Louis Oosthuizen (South Africa); Lee-Ann Pace (South Africa; the only woman to drop); Charl Schwartzel (South Africa); Adam Scott (Australia); Vijay Singh (Fiji); Jordan Spieth (America); Camilo Villegas (Colombia); and Tim Wilkinson (New Zealand) have all dropped. Yahoo Finance will continue to update the tally here.

Many of the golfers, though not all, have pointed to the Zika virus, currently spreading through Brazil, as their reasoning.

Adam Scott, the Uniqlo-sponsored Australian who has won two PGA Tour events this year and is ranked No. 8 in the world, dropped out back in April, citing “an extremely busy playing schedule around the time of the Olympics and other commitments.” Louis Oosthuizen, who would have been guaranteed a spot representing South Africa, cited his schedule. Veteran and three-time Major champion Vijay Singh cited his schedule as well as Zika. In the last week, two of the sport’s very biggest stars, world No. 1 Jason Day of Australia and world No. 4 Rory McIlroy of Ireland, both dropped out and both cited Zika. Marc Leishman of Australia, Charl Schwartzel of South Africa, and Shane Lowry of Ireland, all dropped out and all cited Zika. Dustin Johnson, on July 8, became the first American to drop, and blamed Zika.

But make no mistake: This isn’t entirely (and maybe not even mostly) about Zika.

The International Olympic Committee (IOC) voted to bring back men’s and women’s golf (and rugby) as an Olympic sport in 2009, for the 2016 and 2020 Summer Games. It was last played at the Olympics in 1904. The IOC vote came as something of a surprise to many in the golf world, particularly because golf is such an individual sport. And the structure for Olympic golf somewhat confirms the strangeness of making it an Olympic event: The tournament will be a 72-hole individual play format. Sound familiar? That’s how any other PGA Tour event or Major works. In other words, there’s no twist or unique touch to set Olympic golf apart from the events these players compete in all year.

“There is absolutely no earthly reason that golf should be an Olympic sport,” opined ESPN’s Mike Greenberg last week on his radio show “Mike and Mike.” “There is not a single player in the world who would sooner win Olympic gold in golf than one of the Majors or frankly, probably any of the other events on the PGA Tour. So personally, I don’t know why in the world they’re doing this in the first place and I have no problem whatsoever with McIlroy deciding not to go.”

The golfers themselves agree, judging by comments from many inside the golf world and by the rush of players to opt out. When McIlroy announced he would not go, his open spot became available to Graeme McDowell. But McDowell immediately declined the spot, so quickly it was almost comical. Spieth, world No. 3, took a long time deliberating but decided on July 11 not to go.

Katie Taylor, a gold medalist Irish boxer, criticized her fellow Adidas endorser Jason Day, calling Zika an excuse: “I wonder what excuse the golfers would of made if there was no virus,” she tweeted.

The fear of Zika is real, but it is not the whole story. “Zika is an avatar for a combination of reasons players aren’t interested in going to Rio,” says Matthew Rudy, a senior writer for Golf Digest. “It’s the hassle of going down there. The crammed schedule. The drug testing. The second-class status of a medal compared to a Major. The sponsorship factor. There’s more risk than reward for a player like Rory McIlroy or Jason Day.”

Many of the players have cited their schedules. Indeed, the Open Championship (often called the British Open) begins on July 10, and the PGA Championship is two weeks later, beginning on July 25. The Olympics in Rio begin less than two weeks later, and shortly afterward are a number of important tournaments for the FedEx Cup and, in September, the Ryder Cup. So the Olympics come immediately after two back-to-back Majors. “If you’re Rory, it just isn’t realistic to commit to all that,” says Rudy.

If the Games were taking place somewhere else that is more convenient and a larger media market, such as London, you might see fewer cancellations, insiders say. Money is also an issue: These players, used to having a shot at millions when they play in a Major, are being asked to play for love of country, with no paycheck.

Golf has struggled in recent years to attract a new and younger audience, though it has tried. Golf equipment makers have struggled across the board, with the one-time industry leader, TaylorMade, falling so far that Adidas is now looking to sell it off. Rounds of golf played each year were down for many consecutive years, until last year, according to the National Golf Foundation. More courses in the US close each year than open up.

Golf’s governing bodies had hoped that exposure from the Olympics could help stoke new fan interest in golf. But if the biggest stars aren’t there, that’s unlikely. As IOC member Barry Maister told a New Zealand radio show, “Putting up some second or third rate players is far from the Olympic ideal… Any sport that cannot deliver its best athletes, in my view, should not be there.”

The International Golf Federation (IGF) appears to know the stakes. After Nike-sponsored mega-star McIlroy dropped out, it released a somewhat admonishing statement saying, in part, “The IGF is disappointed with Rory’s decision… As we have stated before, the Olympics is the world’s greatest celebration of sport and we remain excited about golf’s return after a 112-year absence.”

Jack Nicklaus, who has won a record 18 Majors and wields enormous influence in the sport, has said it’s “sad” to see golfers drop out of the Olympics. “I think it’s sad for the Olympics and for the game of golf,” he said. “What I’m concerned about is that golf has a little bit of momentum going right now… If the guys don’t want to participate, then we might not be in the Olympics after this. They vote next year. And if they vote to keep golf in, then that’s great, but if not then we lose that momentum with growing the game.”

Because Johnson and Spieth dropped, the American squad will be Rickie Fowler, Bubba Watson, Patrick Reed and Matt Kuchar. But with Day, McIlroy, Scott, and so many others opting out, the sport’s larger “momentum” Jack Nicklaus is worried about has already been lost.

This story was last updated at 11:16am EST on July 11. We will continue to update it as more golfers opt out of the Olympics.

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Daniel Roberts is a writer at Yahoo Finance, covering sports business and technology. Follow him on Twitter at @readDanwrite.

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